Dual-chamber syringe and methods

ABSTRACT

A dual-chamber syringe has a plunger within an inner delivery chamber in fluid communication with an ejection port. The deliver chamber is formed within a tubular element axially slidable within a tubular guide. The tubular guide and the syringe outer barrel form an outer reservoir chamber. The outer reservoir chamber is sealed from the delivery chamber while the tubular element is in a first position within the guide. Upon withdrawal of the plunger, frictional contact imparted by the plunger seal causes the tubular element to slide away from sealing engagement with the barrel into a second position within the guide. In the second position of the tubular element, a fluid passageway is opened from the reservoir to the delivery chamber allowing fluid to be drawn into the delivery chamber. A porous seal between the plunger rod and barrel allows air into the reservoir during transfer of fluid to the delivery chamber. Pressing the plunger inward first moves the tubular element from the second position back to the first position to close the fluid passageway and then expels fluid from the delivery chamber through the ejection port.

RELATED PATENT APPLICATIONS

This application is a continuation-in-part application of U.S. Ser. No.08/312,878, entitled “Dual-Chamber Syringe & Method,” filed Sep. 27,1994, now U.S. Pat. No. 5,496,284, which is incorporated herein byreference and made a part of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved syringe and, more particularly, toa dual-chambered syringe having a fluid reservoir accessible to adelivery chamber upon axial displacement of a plunger.

2. Background Discussion

In many medical procedures there is a need for locally anesthetizing alarge region subject to an operation or other treatment. Localadministration of anesthetic may require several distinct injections inthe affected area, or injection of a first volume of anesthetic at arelatively shallow depth followed by one or more further injectionsafter advancing the hypodermic needle deeper into the tissue of thepatient, or both. This successive delivery of anesthetic to varyingtissue depths ensures a complete and measured numbing of all of thenerve endings in the treated region.

When delivering a large quantity of any fluid using a syringe, such asin the successive, varying depth injection method, the syringe must havea large capacity, or must be withdrawn intermittently and refilled.Large syringes are cumbersome, and it is often difficult to meter smallquantities with them as the barrel has a large cross-section. Thus, evena small movement of the plunger correlates to a large fluiddisplacement. Even smaller syringes having volumetric graduations usedto inject two or three sequential doses are difficult to meter exactly.Moreover, the smaller the diameter of the syringe, the less pressure isrequired to deliver the injection, and consequently, less pain.Withdrawal of the syringe from an injection site for refilling andsubsequent re-injection is inconvenient and increases the chance ofinfection and trauma to the patient.

There have been efforts in the prior art to provide a dual-chambersyringe for storing a volume of fluid in a reservoir to be transferredinto a delivery chamber, or visa versa. Typically, the fluid is ejectedfrom the delivery chamber through a nozzle by a plunger. There arevarious motivations for providing dual-chamber syringes, includingsimply increasing the syringe capacity, providing a sterileself-contained single-use syringe, and mixing two components prior toinjection, for example. Many of the known devices, however, require theinjection nozzle to be plugged prior to transferring fluid between thereservoir and the delivery chamber. In other known devices, one chamberis placed in communication with another only upon relative rotation ofthe chamber barrels.

One dual-chamber syringe is shown in U.S. Pat. No. 553,234 issued toFinot. This syringe includes a rotatable inner chamber for selectivelycommunicating the inner chamber with either the injection nozzle or thereservoir. Despite the benefit of a larger carrying capacity, thesyringe must be manipulated with two hands to transfer fluid betweenchambers. Further, the syringe of Finot was not designed for successive,varying depth injections which are best accomplished rapidly and withminimum lateral movement.

Despite numerous previous dual-chamber syringe designs, all share thedrawback of requiring a two-handed operation to transfer fluid betweenthe internal chambers. There is thus a need for a dual-chamber syringeparticularly suited for successive, varying depth injections which canbe actuated with one hand.

SUMMARY OF THE INVENTION

The syringe of this invention has several features, no single one ofwhich is solely responsible for its desirable attributes. Withoutlimiting the scope of this invention as expressed by the claims whichfollow, its more prominent features will now be discussed briefly. Afterconsidering this discussion, and particularly after reading the sectionentitled, “DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT,” one willunderstand how the features of this invention provide its benefits,which include one-handed operation; convenience of use; larger capacity;successive, varying depth injection of anesthetic; ease of introductionof medication into dense tissue; better control of quantity ofanesthetic used, thereby avoiding unnecessary tissue swelling;filtration of air introduced into syringe; the use of a single needle togive multiple injections without the need to remove the needle from thebody of the patient; reduction of pain during injection because smallerdiameter needles may be used; and elimination of vials holdingmedication, thereby reducing of likelihood contamination.

The first feature of the medical syringe of this invention is that itincludes a plunger having at one end a resilient seal, and a barrelhaving a central longitudinal axis and a pair of opposed ends. Theplunger has at an end remote from the end with the resilient sealthereon a thumb ring, and the barrel has at least one external fingerrest. The barrel has at one end an ejection port and at the other end anopening. Preferably, the opening in the barrel has a porous seal whichsurrounds the plunger. This porous seal allows air to enter the barrelyet inhibits the flow of liquid from the chamber. The ejection port andopening are aligned with each other and disposed along the longitudinalaxis.

The second feature is outer and inner telescopic tubular elements seatedinside the barrel to be coaxial with the longitudinal axis. The outertubular element is mounted in a stationary position while disposed inthe barrel and the inner tubular element is movable axially within theouter tubular element. The outer tubular element and barrel form achamber which holds a reservoir of liquid. The outer tubular element hasa fluid passageway therein that allows the liquid to flow from thechamber into the inner tubular element. The inner tubular element has anend nearby the injection port with a seal thereon that has an orificetherein. This inner tubular element receives the end of the plunger withthe resilient seal thereon.

The third feature is that the resilient seal fits snug within the innertubular element to grip the inner tubular element. In response to axialmovement of the plunger, the inner tubular element is moved between afirst and second positions. In the first position, the seal with theorifice therein seals the injection port as the plunger is moved towardsthe injection port, preventing liquid in the chamber from passing intothe inner tubular element and forcing any liquid in the inner tubularelement through the orifice and out the injection port. In the secondposition, the seal with the orifice therein is moved to a retractedposition away from the injection port, allowing liquid to flow from thechamber through the passageway and through the orifice into the innertubular member.

The fourth feature is that the plunger is initially in a forwardposition that forces the seal with the orifice therein into engagementwith the injection port to seal this port. Preferably, there is a safetyseal on the plunger which is broken by movement of the plunger into aretracted position, pulling the seal with the orifice therein away fromthe injection port. This thereby initially fills the inner tubularelement with liquid from the chamber. preferably, the barrel and innerand outer tubular elements are made of a transparent or translucentmaterial.

In another embodiment of this invention, a back flow seal is disposed inthe ejection port preventing fluid from entering or leaving said barrelthrough said ejection port. The back flow seal forms a distal boundaryof a refill chamber within said barrel. In this embodiment, the innertubular element has at its distal end a needle having a distal tip. Inresponse to axial movement of the plunger, the inner tubular elementmoves between a first position where said distal tip of the needle islocated within said refill chamber allowing fluid to be drawn throughthe distal tip into the inner tubular element by proximal movement ofthe plunger relative to the inner tubular element, and a second positionwhere said distal tip extends through said back flow seal into theejection port allowing fluid to be expelled through said ejection portupon distal movement of the plunger relative to the inner tubularelement. Preferably, there is a safety seal on the plunger which must bebroken before the plunger may move with respect to the barrel.

This invention also includes a method of giving an injection of ananesthetic into the body of a patient. This method includes the steps of

(a) providing a syringe with a reservoir that contains the anestheticand a delivery channel which receives a plunger which when moved in onedirection places the channel in communication with the reservoir and inanother direction discontinues the communication and ejects anestheticfrom the channel,

(b) initially introducing the anesthetic using the syringe into the bodyof the patient, and

(c) introducing a second dosage of the anesthetic by moving the plungerin the one direction to place the reservoir into communication with thechannel and refill the channel with anesthetic and then moving theplunger in the other direction to discontinue the communication andeject anesthetic from the channel.

This invention also includes a method of giving of a medication into thebody of a patient, including the steps of

(a) providing a syringe with a reservoir that contains the medicationand an inner tube defining a delivery channel, said tube having a needleon one end and a plunger received in the opposite end, said plungerplacing the needle in communication with the reservoir when moved in onedirection and discontinuing the communication and ejecting medicationfrom the channel when moved in another direction, and

(b) using the syringe initially to introduce the medication into thebody of the patient, and

(c) introducing a second dosage of the medication by moving the plungerin the one direction to place the reservoir into communication with theneedle and refill the channel with medication and then moving theplunger in the other direction to discontinue the communication andeject medication from the channel.

This invention also includes a method of injecting fluid from a syringe,including the steps of

withdrawing a plunger to displace an inner tubular element into a firstposition within said syringe, said tubular element having a needlethereon, the needle reversing out of a back flow seal mounted in anejection port by movement of the tubular element into said firstposition,

withdrawing said plunger to displace an inner resilient seal withrespect to the tubular element creating a reduced pressure within saidtubular element and drawing fluid therein through said needle from areservoir formed outside of said tubular element,

depressing said plunger to displace the inner tubular element into asecond position within said syringe, said needle piercing said back flowseal to reach said ejection port by movement of the tubular element intosaid second position, and

depressing said plunger to displace said inner resilient seal withrespect to the tubular element creating an elevated pressure within saidtubular element and expelling fluid therein through said needle intosaid ejection port.

In these methods only one hand is used to manipulate the syringe.

DESCRIPTION OF THE DRAWING

The preferred embodiment of this invention, illustrating all itsfeatures, will now be discussed in detail. This embodiment depicts thenovel and non-obvious syringe and methods of this invention as shown inthe accompanying drawing, which is for illustrative purposes only. Thisdrawing includes the following figures (Figures), with like numeralsindicating like parts:

FIG. 1a is a perspective view of a dual-chamber syringe of the presentinvention during delivery of fluid to an injection site through aneedle.

FIG. 1b is a perspective view of the dual-chamber syringe of FIG. 1during transfer of a fluid from an internal reservoir to a deliverychamber.

FIG. 1c is an enlarged perspective view of a distal end of the syringein FIG. 1b showing fluid flow from the reservoir into the deliverychamber.

FIG. 2a is an exploded, perspective view of the dual-chamber syringe ofFIG. 1 showing the components of the syringe.

FIG. 2b is an enlarged perspective view of a proximal end of thedual-chamber syringe of FIG. 1 prior to rupture of a safety seal;

FIG. 2c is an enlarged perspective view similar to FIG. 2b after thesafety seal has been ruptured;

FIG. 3 is another exploded, perspective view of the syringe of FIG. 1showing the components of the syringe.

FIG. 4 is a cross-sectional view of the syringe of FIG. 1 duringtransfer of fluid from an internal reservoir to a delivery chamber.

FIG. 5 is a cross-sectional view of the syringe of FIG. 1 duringdelivery of a fluid through an ejection port.

FIG. 6 is a cross-sectional view of an alternative embodiment of adual-chamber syringe of the present invention prior to an initial usethereof.

FIG. 7 is a cross-sectional view of the syringe of FIG. 6 duringdelivery of a fluid through an ejection port.

FIG. 8 is a cross-sectional view of the syringe of FIG. 6 duringtransfer of fluid from an internal reservoir to a delivery chamber.

FIG. 9 is a cross-sectional view of a further embodiment of adual-chamber syringe prior to an initial use thereof.

FIG. 10 is a perspective view of a whole calibrated dose meter for usewith the dual-chamber syringe of FIG. 6.

FIG. 11 is a perspective view of the dose meter of FIG. 10 with severalcalibrated segments broken away.

FIG. 12 is an exploded, perspective view of a further embodiment of adual-chamber syringe adapted to be used In conjunction with the dosemeter of FIG. 10.

FIG. 13 is a detailed, cross-sectional view of the syringe of FIG. 12prior to installation of the dose meter.

FIG. 14 is a detailed, cross-sectional view of the syringe of FIG. 12during delivery of a fluid through an ejection port.

FIG. 15 is a detailed, cross-sectional view of the syringe of FIG. 12during retraction of the plunger until restricted from further movementby the dose meter.

FIG. 16 is a detailed, exploded, perspective view of the proximal end ofthe syringe of FIG. 16 within the circle of FIG. 12 illustrating theplacement of the dose meter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1a, a first embodiment of a dual-chamber medicalsyringe 20 includes an outer tubular barrel 22 including a distal end 24and a proximal end 26. The distal end 24 includes a tapered section 28leading to a stem 30 for receiving a hub 32 of a needle 34. Thoseskilled in the art will understand that the stem 30 is of a generallystandard type in the medical industry, and various needles and the likewill be readily received thereon.

The proximal end 26 of the barrel 22 is covered by an end cap 36 havingan aperture 86 (FIG. 3) for receiving a plunger 38. The plunger 38includes a plunger rod 40, as seen in FIG. 1b, and a thumb ring 42 onits proximal end. The barrel 22 further includes a first pair ofoutwardly extending finger rests 44 adjacent to the end cap 36 and asecond pair of outwardly extending finger rests 46 proximally disposedwith respect to the first pair. Additionally, a series of externalcircumferential grip ribs 48 are formed on the barrel 22 between thefinger rests 44, 46.

The syringe 20 is thus configured to allow a medical technician toinsert a thumb 50 through the thumb ring 42 while gripping the barrel 22with the index and middle fingers 52 in the general location of the ribs48. The syringe 20 exhibits both finger rests 44 and 46 to allow anoperator to displace the thumb ring 42, and associated plunger rod 40,in either axial direction with respect to the barrel 22. FIG. 1a showsthe needle 34 after having pierced an injection site 54. Movement of theplunger 38 in the direction of arrow 56 relative to the barrel 22 forcesfluid out of the needle 34, as shown by arrows 58. Advantageously, thisone-handed operation facilitates rapid and steady, successive, varyingdepth injections, as will be more fully explained below.

Looking now at FIG. 2a, the cylindrical barrel 22 is sized to receive achannel member or tubular guide 60 which, in turn, receives a tubularelement 62. When assembled, the three tubular elements 22, 60 and 62 fitconcentrically within one another along a common longitudinal axis 64.The tubular guide 60 is slightly longer than the tubular element 62.When assembled, as shown in FIG. 4, the proximal end of the guide member60 contacts the end cap 36, and distal end abuts the tapered section 28.The tubular element 62, on the other hand, is free to slide axiallywithin the guide member 60 a short distance, the reason for which willbe explained further below.

The tubular guide 60 includes a pair of diametrically opposed axialslots 66 in the distal end and a plurality of axial slots 68 in theproximal end. The tubular element 62 is fitted with an elastomeric,plunger-like seal 70 on its distal end having an orifice 72therethrough. A large portion of the tubular element 62 is marked with aseries of volumetric graduations 74. A breather slot 76 is formed in thedistal end of the tubular element 62.

The plunger 38, as shown exploded in FIG. 3, includes a resilient fluidseal 78 attached to the distal end. A porous sleeve or seal 80 fitssnugly around the plunger rod 40 intermediate the seal 78 and a stopring 82. The end cap 36 is defined by a flat disk portion 83 sized tocover the proximal end of the barrel 22 and a circular flange 84extending in a proximal direction. A central throughbore 86 of the endcap 36 receives the plunger rod 40. The throughbore 86 is sized to fitsnugly over the porous seal 80. As seen in FIG. 4, the porous seal 80fills the annular space between the piston rod 40 and the throughbore 86of the end cap 36.

A safety seal 88 is provided for packaging and safe transport of thesyringe 20 while carrying liquid. More particularly, the plunger 38assumes a fully depressed position during transport with the stop ring82 juxtaposed against the circular flange 84, as shown in FIG. 2b. Thesafety seal 88, which may be, for example, one-sided tape, is adheredaround the junction of the stop ring 82 and flange 84. A perforatedcircle 90 is provided around the mid-portion of the safety seal 88. Uponfirst twisting and then moving of the plunger 38 in the direction ofarrow 91 in FIG. 2c, the perforated circle 90 is ruptured allowing thesyringe 20 to operate as desired. As indicated, the rupture of theperforated circle 90 may be facilitated by rotating the thumb ring 42and integral stop ring 82 relative to the barrel 22.

Now looking at FIGS. 4 and 5, the outer barrel 22 includes a thickenedregion 92 adjacent the stem 30. The thickened, region 92 has an innertapered surface 94. At the proximal end of, the region 92, a circularledge 96 forms a contact and centering ring for the tubular guide 60.The annular space between the tubular guide 60 and the barrel 22 definesan outer fluid chamber or reservoir 98. The reservoir 98 serves as theprimary receptacle for storing liquid medication, such as an anesthetic,or other fluid to be injected. However, due to the presence of the axialslots 68 and 76, fluid can freely pass between the reservoir 98 and aproximal portion 99 of the interior of the tubular element 62, althoughthe syringe 20 is intended to function best with the majority of fluidremaining in the reservoir.

The resilient seal 70 on the distal end of the tubular element 62 has aforward taper 100 configured to seal against the tapered surface 94 ofthe barrel 22. As mentioned above, the tubular element 62 has an axiallength such that it may move a short distance between the taperedsurface 94 and the end cap 36 and within the confines of the guide 60.

The resilient seal 78 divides the inner volume of the tubular element 62into a distal portion or delivery chamber 102 and the proximal portion99. Thus, the delivery chamber 102 is in fluid communication with anejection port 116 in the stem 30 when the tubular element 62 is in adistal position and the seal 70 is engaged with the tapered surface 94as shown in FIG. 5. In this position, the seal 70 prevents fluid frompassing between the reservoir 98 and the delivery chamber 102. Thetubular element 62 may be displaced proximally into a second positionshown in FIG. 4 wherein the seal 70 is disengaged from the taperedsurface 94. In this second position, fluid may travel through apassageway 110 between the tapered surfaces 94 and 100. Thus, only whenthe tubular element 62 is slid into the second position can fluid travelfrom the reservoir 98 to the delivery chamber 102.

Assembly of the Syringe of FIG. 1

The present syringe 20 is designed to be filled with anesthetic or otherfluid prior to final assembly and then transport to a hospital ormedical facility for use. More particularly, the syringe 20 is assembledby first inserting the tubular guide 60 into the barrel 22 until thedistal end contacts and seats on the circular ledge 96. Next, thetubular element 62 is slid within the guide 60. After assembling theporous seal 80 and end cap 36 over the stem 40, the plunger 38 isinserted into the tubular element 62, with resilient seal 78 being firstplaced into the tubular element. With the seal 70 of the element 62pressed against the tapered surface 94, anesthetic or other fluid 106 isadded to the reservoir 98 between the guide 60 and barrel 22. The diskportion 83 of the end cap 36 is then bonded to the proximal rim of thebarrel 22. The means for bonding the cap 36 to the barrel 22 may beadhesion, heat seal, ultrasonic welding or other similar expedient.Finally, the plunger 38 is fully depressed so that the stop ring 82comes into contact with the flange 84, whereupon the safety seal 88 issecured around the two components with the perforated circle 90 lined upin the junction plane.

The syringe 20 is then sealed from external contamination by the end cap36, safety seal 88 and contact between seat 70 and tapered surface 94. Aprotective cap (not shown) may be attached over the stem 30 to preventcontamination in the ejection port 116.

Operation of the Syringe of FIG. 1

In order to use the syringe 20, the safety seal 88 is first ruptured atthe perforated circle 90 by a twisting motion of the thumb ring 42relative to the barrel 22, as seen in FIG. 2c. At this point, fluid 106remains within the reservoir 98 by the contact between the seal 70 andtapered surface 94. Proximal movement of the plunger 38 as seen by arrow108 creates friction between the resilient seal 78 and the inner surfaceof the tubular element 62. This friction causes the tubular element 62to be displaced in a proximal direction, opening up the fluid passageway110 between the seal 70 and tapered surface 94. After the tubularelement 62 contacts the end cap 36, further movement of the plunger 38creates a suction or reduced pressure in the delivery chamber 102. Thissuction pulls fluid 106 into the delivery chamber 102 from the reservoir98. The fluid flow, as shown by arrows 112, passes through the axialslots 66, the fluid passageway 110 and orifice 72. During proximalmovement of the plunger 38, air is introduced into the barrel 22 throughthe porous seal 80, as shown by arrows 114 in FIG. 4. The frictionalsurface contact with the flange 84 maintains the position of the porousseal 80 while allowing the plunger rod 40 to slide relative thereto.

When the delivery chamber 102 is filled, the medical technician bleedsany air therein and expels anesthetic through the ejection port 116until the proper volume remains, as indicated by the graduation markings74. in order to view fluid against the graduated markings 74, the barrel22, tubular guide 60 and tubular element 62 are formed of transparent ortranslucent materials. After advancement of the needle 34 a first depthinto the injection site 54, anesthetic is expelled though the ejectionport 116 by distal movement of the plunger 38 via the thumb ring 42, asshown by movement arrow 56 in FIGS. 1a and 5. Initial distal movement ofthe plunger seal 78 urges the tubular element 62, and more specificallythe seal 70, into engagement with the tapered surface 94 of the barrel22. This closes off the fluid passageway 110 between the reservoir 98and the delivery chamber 102. Further movement of the plunger 38 thusforces fluid from the delivery chamber 102 until the resilient seal 78bottoms out against the inner surface of the seal 70.

After a first infusion of anesthetic at the first depth of the needle34, the syringe 20 is advanced to position the needle at a second depth.At this point, the plunger 38 is again withdrawn relative to the barrel22 via the thumb ring 42 and finger rest 46. After the frictionalcontact of the resilient seal 78 pulls the tubular element 62 againstthe end cap 36, and upon further proximal movement of the plunger 38, anegative pressure develops within the delivery chamber 102. Due to theproximal movement of the tubular element 62, the fluid passageway 110 isonce again opened for anesthetic to flow along the path of arrows 112 inFIG. 4 through the orifice 72 and into the delivery chamber 102. In thismanner the syringe 20 is once again primed and ready to deliver anotherinfusion of anesthetic at the second needle depth.

This process can be repeated at successive depths until the injectionsite is sufficiently numbed, or until the anesthetic in the reservoir 98is exhausted. The entire sequence of infusion-advance-prime-infusion caneasily be accomplished with the thumb and fingers of only one hand.Furthermore, the priming and expulsion of fluid from the deliverychamber 102 is done by simply advancing and retracting the plunger 38along the axis of the syringe 20.

Another benefit of the present syringe 20 is the large capacity of thereservoir 98 in combination with the relatively small force required toinfuse fluid into the patient. More particularly, the inner diameter ofthe tubular element 62 is preferably between 1.0 and 1.5 cm. This smallsize enables the operator to generate a large pressure within thedelivery chamber 102 with the application of only small forces on thethumb ring 42. At the same time, the barrel 22 may have an innerdiameter of between 2 and 3 times the diameter of the tubular element62, resulting in a large fluid storage capacity available to thedelivery chamber 102. Conversely, the small diameter of the tubularelement 62 also enables the operator to generate a large negativepressure in the delivery chamber 102 making it easy to prime the syringe20 for another injection. In other words, it is easy to suck fluid intothe delivery chamber 102. This helps reduce fatigue to the hands of theoperator during a large number of repetitive injections.

The initial priming of the syringe 20 is preferably done external to theinjection site 54. The protective cap (not shown) over the stem 30 sealsthe ejection port 116 to enable the plunger 38 to pull fluid into thedeliver chamber 102 from the reservoir 98, rather than air in throughthe ejection port. After the needle 34 has been buried in the injectionsite 54, the small size of the needle orifice provides sufficientresistance to entry into the needle 34 of relatively viscous bodilyfluids. The negative pressure required to pull fluid 106 into thedelivery chamber 102 is primarily related to the resistance of airpassage through the porous seal 80. Thus, the seal 80 is designed toexhibit less resistance to air passage than the resistance of the needleorifice to bodily fluids.

Dual-Chamber Syringe With Back-Flow Seal

As shown in FIG. 6, a second embodiment of a dual-chamber medicalsyringe 120 includes an outer tubular barrel 122 having a distal end 124and a proximal end 126. The distal end 124 includes a tapered section128 leading to a stem 130 for receiving a hub 132 of a needle 134.Again, the stem 130 is of a generally standard type in the medicalindustry, and various needles and the like will be readily receivedthereon.

The proximal end 126 of the barrel 122 is covered by a disk-shaped endcap 136 having an aperture 137 for receiving a plunger 138. The plunger138 comprises a plunger rod 140 having a resilient plunger seal 142fitted to a distal end, and a thumb ring 144 on its proximal end. Theplunger rod 140 is sized to fit closely through the aperture 137, or asmall gap may be provided for passage of a dose metering stick, as willbe explained below. The barrel 122 further includes first and secondpairs of outwardly extending finger rests 146 adjacent to the end cap136, as well as a series of external circumferential grip ribs 148formed on the barrel 122 between the finger rests. As with the firstembodiment, the syringe 120 is configured to allow a medical technicianto insert a thumb through the thumb ring 144 while gripping the barrel122 with the index and middle fingers in the general location of theribs 148. The syringe 120 exhibits proximal and distal finger rests 146to allow an operator to displace the thumb ring 144, and associatedplunger rod 140, in either axial direction with respect to the barrel122.

Looking now at FIGS. 6 and 7, a channel member or tubular guide 150concentrically fits within the tubular barrel 122. The guide 150 istubular along its entire length until a distal taper 152 leading to atubular neck 154. One or more axial slots 156 are formed along the neck154 and extend to the distal tip abutting a thickened region 158 (FIG.7) of the barrel 122. A resilient guide plug 159 is sized to engagefirmly the solid portions in the distal tip of the neck 154 in advanceof the slots 156, and is positioned so that liquid does not enter theinterior of a tubular element 162 that receives the plunger 138. Theproximal end of the tubular guide 150 contacts the end cap 136, and thedistal end of the neck 154 abuts an annular surface 160 (FIG. 7) definedby a proximal face of the thickened region 158. The guide 150 is held ina fixed position within the barrel and is solid along its length exceptfor the slots 156.

The tubular element 162 has a diameter slightly smaller than the tubularguide 150 and it includes a proximal tubular region and a tapered distalend 164 on which a needle or cannula 166 mounts. The cannula 166 extendsdistally to a tip 168. The tubular element 162 has an axial length froma proximal end 165 to the tapered end 164 shorter than the interiorclearance within the tubular guide 150. The tubular element 162 can thusslide freely within the guide 150 between the end cap 136 and taper 152.in this respect, FIG. 6 illustrates the tubular element 162 in a first,proximal position within the guide 150 with the proximal end 165abutting the end cap 136. FIG. 7 shows the element 162 in a second,distal position within the guide 150 with the tapered end 164 restrictedby the taper 152. Preferably, the angles formed with the longitudinalaxis by the taper 152 and tapered end 164 are identical. The plungerseal 142 forms a friction fit with the interior walls of the tubularelement 162 such that movement of the plunger 138 displaces the tubularelement 162 within the guide 150.

A back flow seal 170 firmly engages the interior walls of an ejectionport 174 within the stem 130 of the barrel 122. In the first, proximalposition of the tubular element 162, the tip 168 of the cannula 166extends through the resilient guide plug 159 and into a refill space orchamber 172 formed between the back flow seal 170 and guide plug. In asecond, distal position of the tubular element 162 the tip 168 of thecannula 166 extends through the back flow seal 170 and into the ejectionport 174. The longitudinal movement of the tubular element 162 is causedby longitudinal movement of the plunger 138, as will be explained inmore detail below.

FIG. 6 shows an intact safety seal 176 provided for packaging and safetransport of the syringe 120 while carrying liquid, while in FIG. 7 theseal 176 has been removed. The plunger 138 assumes a position duringtransport with a stop ring 178 held away from the end cap 136 by acylindrical spacer 180 secured in position by the seal 176. The safetyseal 176, which may be, for example, one sided tape, is adhered aroundthe junction of the stop ring 178 and spacer 180. A pull tab is providedto remove the seal 176 and spacer 180, which is preferably constructedof thin plastic or other biocompatible material. The spacer 180 isdesigned to have sufficient column strength while supported by the outerseal 176 to prevent distal movement of the stop ring 178 toward the endcap 136 during shipping, yet be relatively fragile and easy to removeonce the seal 176 has been peeled away in preparation for use of thesyringe 120. Alternatively, the safety seal 176 itself may incorporatethe spacer 180.

Operation of the Syringe With Back-Flow Seal

The syringe 120 holds an initial dose of medication such as, forexample, insulin or anesthetic, within a delivery chamber 182 (FIG. 6)defined inside the tubular element 162 between the plunger seal 142 andthe needle tip 168. The spacer 180 enables the plunger 138 to maintainthis retracted position during shipping. After the seal 176 is removed,and the syringe needle 134 is positioned at a desired location in apatient, the plunger 138 may be actuated by the operator via the thumbring 144, finger rests 146 and grip ribs 148 in the direction of arrow184. Initial distal movement of the plunger 138 urges the tubularelement 162 from its first, proximal position seen in FIG. 6 to thesecond, distal position of FIG. 7 by virtue of the friction between theplunger seal 142 and interior walls of the tubular element 162.Specifically, the tapered end 164 is displaced into engagement with thetaper 152 of the guide 150. The needle tip 168 pierces the back flowseal 170 and enters the ejection port 174. Further movement of theplunger 138 forces fluid from the delivery chamber 182 until the plungerseal 142 bottoms out against the tapered end 164, or the stop ring 178contacts the end cap 136. The fluid travels through the ejection port174 as indicated by arrow 186 and is expelled from the needle 134.

The dual-chamber syringes of the present invention are especially suitedfor repeat injections at different depths, as indicated above. This isaccomplished in the syringe 120 by storing a reserve supply of fluid inan outer reservoir 192 formed within the barrel 122 and outside of thetubular guide 150. The placement of the slots 156 is such to preventcommunication between the reservoir 192 and interior of the tubularguide 150.

FIG. 8 illustrates the syringe 120 during retraction of the plunger 138to refill the delivery chamber 182. Initial retraction of the thumb ring144 in the direction of arrow 188 displaces the tubular element 162 fromits second, distal position to its first, proximal position with theproximal end 165 abutting the end cap 136. The needle tip 168 is thuslocated within the refill chamber 172 in communication with the fluid inthe reservoir 192. Further retraction of the plunger 138 creates areduced pressure within the chamber 182 from the rearward movement ofthe plunger seal 142, drawing fluid into the tip 168, as indicated byarrows 194. The tubular element 162 may be calibrated to show theoperator the volume of fluid therewithin, or a separate dose meter,described below, may be utilized to signal when a desired volume hasbeen drawn into the delivery chamber 182. The process is repeated for asmany times as necessary, or until the fluid within the reservoir 192runs out, which lasts significantly longer than previous single-barrelsyringes.

During the entire process, the cannula needle 168 remains centered bythe resilient guide plug 159 to ensure repeated punctures through thecenter of the back flow seal 170. Additionally, the back flow seal 170prevents fluid from being drawn into the syringe 120 through theinjection needle 134 when the plunger 138 is being withdrawn to refillthe delivery chamber 182.

Alternative Self-Locking Feature

FIG. 9 illustrates a syringe 200 which is similar in many respects tothe syringe 20 of FIG. 1. An outer barrel 202 concentrically contains atubular guide 204 having proximal slots 206, and a tube 208 capable ofsliding axially therewithin. The tube 208 defines a valve 210 on adistal end having a central throughbore 212. A plunger 216 including aresilient member 218 on one end actuates the tube 208 axially within theguide 204 to open and close the valve 210, alternatively allowing andrestricting fluid communication between an outer fluid reservoir and theinterior of the tube 208. In a departure form the previous embodiment,an O-ring seal 214 is located within the space between the guide 204 andtube 208. The seal 214 prevents fluid from traveling proximally to anunsealed aperture 219 in an end cap 221 where the plunger 216 enters thesyringe, thus preventing unwanted leakage therefrom. Additionally, thesyringe 200 incorporates a safety seal 220 for shipping and stop ring222, both of which are similar to those previously described withrespect to FIG. 6. The plunger 216 additionally includes self-lockingstructure 224 which mates with locking tabs attached to the end cap 221of the syringe 200. The specific locking structure will be more fullydescribed and shown in detail below with respect to a furtherembodiment. The locking structure 224 more securely maintains theplunger 216 in its initial position during shipping, and in that respectsupplements the safety seal 220.

Dual-Barrel Syringe With Automatic Dose Meter

FIG. 10 shows an intact dose meter 230 for use with any of the presentdual-barrel syringes. The dose meter 230 enables the operator toautomatically sense the correct dose when refilling the plunger deliverychamber without visual inspection. This is particularly Important whentime is critical, and also when the doses are small, and manuallymetering the correct amount becomes more difficult.

The dose meter 230 comprises a split ring 232 forming nearly a completecircle and a calibrated stick 234. The stick 234 extends in an axialdirection from a portion of the ring 232 opposite the split. As seen inFIG. 11, the calibrated stick 234 includes a plurality of identicalcalibrated segments 236 separated by weakened separation lines 238. Thestick 234 may be shortened from an initial length by breaking off one ormore segments 236 from the free end, as indicated in FIG. 11.

FIGS. 12 and 16 show the placement of the dose meter 230 in relation tothe dual-barrel syringe 120 of the present invention. After theaforementioned seal 176 has been removed and the plunger 138 retracted ashort distance, the split ring 232 is spread apart to pass around andencircle the plunger stem 140. The calibrated stick 234 has an arcuatecross-section facilitating insertion into the small gap between the stem140 and central aperture 137 through the end cap 136.

FIG. 13 shows the dose meter in an initial position prior to beingaffixed in place on the syringe 120. The split ring 230 includes a rib242 extending radially inward from an outer wall portion 244. The endcap 136 includes a pair of axial fingers 246 (best seen in FIG. 16)diametrically opposed across the central aperture 137 and terminating inoutward detents 248. The detents 248 are sized and shaped to interferewith the rib 242. The locking structure 224 mentioned above withreference to the embodiment of FIG. 9 is similar to the mating rib 242and detents 248. The split ring 232, as well as the end cap 222 there,can be unlocked from the syringe by firm proximal movement to disengagethe rib 242 and detents 248. In this respect, the fingers 246 arerelatively thin so that any such cam action against the detents 248bends the fingers fairly easily inwardly.

FIGS. 14 and 15 depict the use of the dose meter 230. Prior to use, theoperator slides the split ring 232 distally to cam the rib 242 over theopposed detents 248. This can be accomplished during the initialdelivery of fluid with the plunger 138, as indicated by the arrow 250 inFIG. 14. The dose meter 230 is thus held in a fixed axial location withrespect to the end cap 136.

In the normal mode of operation, the dose meter 230 remains in place,with the unbroken portion of the calibrated stick 234 extending alongthe plunger stem 140 within the tubular element 162. Retraction of theplunger 138 in the direction of arrow 252 draws fluid into the deliverychamber 182, as mentioned previously. Because the concentric tubularmembers are transparent, volumetric markings 240 (FIG. 12) on thetubular element 162 may be visually monitored to determine the correctamount of fluid drawn therein. Preferably, however, the operator relieson the dose meter 230 to signal the when the correct dose has been drawninto the delivery chamber 182. Because the plunger seal 142 is notdisplaced with respect to the tubular element 162 until the proximal end165 contacts the end cap, the movement of the plunger seal in drawingfluid can be measured relative to the dose meter 230 fixed with respectto the end cap 136. The stick 234 is calibrated to restrict the plungerseal 142 movement when a predetermined volume of fluid is drawn into thedelivery chamber 182. Thus, as seen in FIG. 15, the plunger 138 cannotbe retracted any farther, and a known quantity of fluid is temporarilystored in the delivery chamber 182. The fluid is then ejected from thesyringe 120 and a new dose drawn into the delivery chamber 182 from thereservoir 192. This procedure can be repeated without the need ofvisually inspecting and estimating the volume of fluid within thetubular element 162. Such convenience is especially important whenanesthetizing a deep area with a series of drug deliveries at successivedepths. The dose meter 230 is thus a simple, reliable and accurate meansfor ensuring the correct amount of fluid is delivered for a successionof injections.

SCOPE OF THE INVENTION

The above presents a description of the best mode contemplated ofcarrying out the present invention, and of the manner and process ofmaking and using it, in such full, clear, concise, and exact terms as toenable any person skilled in the art to which it pertains to make anduse this invention. This invention is, however, susceptible tomodifications and alternate constructions from that discussed abovewhich are fully equivalent. For example, the outside of the syringe maybe marked to indicate the amount of fluid injected into a patient; thereservoir may be divided into separate compartments, each holding onecomponent of a two component medication system; and the reservoir may becharged with a gas to create positive pressure within the reservoir,eliminating the filter/seal. Consequently, it is not the intention tolimit this invention to the particular embodiments disclosed. On thecontrary, the intention is to cover all modifications and alternateconstructions coming within the spirit and scope of the invention asgenerally expressed by the following claims, which particularly pointout and distinctly claim the subject matter of the inventions

What is claimed is:
 1. A medical syringe including a barrel with anejection port at one end and a chamber holding a reservoir of liquidcomprising, an internal partition member within said barrel that atleast partially defines a channel terminating at the ejection port, amoveable tubular element seated within the channel and has an end nearbythe injection port, a fluid passageway which allows the liquid to flowfrom the chamber into the tubular element, a plunger seated within thetubular element, having an end in the tubular element to which isattached a seal, said seal fitting snug against the tubular element togrip said tubular element and, in response to movement of the plunger,to move the tubular element between a first position where the injectionport is sealed and the passageway is blocked to prevent liquid in thechamber from passing into the tubular element, and a second retractedposition where the passageway is unblocked to allow liquid in thechamber to flow from the chamber through the passageway into the tubularmember, said plunger as it is moved from the second retracted positiontowards the ejection port forcing any liquid in the tubular element outthe injection port.
 2. The medical syringe of claim 1 where there is anopening in the barrel having a porous seal which surrounds the plunger,said porous seal allowing air to enter the barrel yet inhibits the flowof liquid from the chamber.
 3. The medical syringe of claim 1 where theplunger is initially in the first position and there is a safety seal onthe plunger which is broken by movement of the plunger into the secondretracted position.
 4. The medical syringe of claim 1 where the chamberat least partially surrounds the channel.
 5. The syringe of claim 1where the amount of liquid drawn into the tubular element is limited bya dose meter.